The present day flow measurement technology employs a volume flowmeter to measure the volume rate of flow, a mass flowmeter to measure the mass rate of flow, and a density meter to measure the density of fluid. The economic models of flowmeters and density meters are not acceptable in many applications requiring accurate measurements as the accuracy and reliability of the economic models are usually very poor. The high quality models of the instruments are quite expensive and, consequently, it is not desirable in terms of economy to purchase many single function instruments to measure different flow variables such as the volume flow, mass flow and the fluid density. In todays chemical, mineral, food and pharmaceutical processing industries, there is a very strong demand for multifunction instruments, which measure more than one flow variable in an accurate and reliable manner.